1. Field of the Invention
The invention relates generally to air interface testing of wireless communication devices and more particularly to systems and methods for a closed field antenna used for such testing.
2. Background
A wireless communication device typically includes a Radio Frequency (RF) port, or RF connector, that can be used to test the RF performance of the device. When using the RF port to test the device, a xe2x80x9ctesterxe2x80x9d is interfaced to the device via the RF port. RF signals are then sent to the device and are received from the device through the RF port. The RF port, therefore, typically bypasses the device""s antenna, which is an important factor in the RF performance of the device. Therefore, to fully test the device""s RF performance, the antenna must be taken into account. This is accomplished through testing known as xe2x80x9cair interface testing.xe2x80x9d An air interface test is designed to test the RF performance of a wireless communication device by sending RF signals to, and receiving RF signals from, the devices antenna.
Unfortunately, simulating the air interface in a manufacturing or test facility is a challenging task. First, the device under test (DUT) must be isolated from external, interfering signals that can cause erroneous test results. This is especially important in the factory, where many devices are being tested simultaneously. Second, the DUT must also be isolated from reflections of its own signals, which can cause self-interference, or self-jamming. In a confined environment, RF signals transmitted by a DUT can reflect off of near by objects and interfere with the test, causing erroneous result much like interfering signals from other devices.
In order to combat interference from externally generated signals, the DUT is typically placed inside a metal isolation box. The box prevents the externally generated signals from interfering with the air interface testing of the DUT. Unfortunately, the box makes the second problem, i.e., self-jamming, worse, because the inside of the box reflects the signals transmitted by the DUT. Therefore, the inside of the box is usually covered with RF absorbing material. But the RF absorbing material is very expensive and it is very difficult to achieve adequate absorption.
Another problem with conventional systems is a lack of reliability and repeatability of test results. This is partly due to the varying isolation and absorbing properties of different test boxes. It is also partly due to the alignment of the DUT within the box, which as a result of conventional test box designs is critical to achieving accurate results. In practice, however, it is very difficult to achieve accurate alignment tolerances with most conventional test boxes. Therefore, alignment issues and interference from internal and external signals makes it difficult to achieve repeatable, reliable test data that can be correlated from one test fixture to the next.
Due to the forgoing, conventional test fixtures/boxes tend to be large, expensive units that fail to produce reliable, repeatable, and comparable test data. Thus, correlation of test results for all DUTs across all test fixtures in a particular factory, for example, is difficult if not impossible.
In one aspect of the invention a tester useful for combating the above problems comprises a first antenna that includes a cylinder formed from a dielectric material, a ground plane covering at least a portion of the outer surface of the cylinder, and a conductor covering a portion of the inner surface of the cylinder and located at approximately the axial midpoint of the center. The tester also includes a test fixture for holding a device under test and interfacing it with the first antenna.
In one embodiment, the test fixture is configured to hold the device under test, which comprises a second antenna, and position the device under test such that the second antenna is substantially within the cylinder.
Other aspects, advantages, and novel features of the invention will become apparent from the following Detailed Description of Preferred Embodiments, when considered in conjunction with the accompanying drawings.